Stressed barrier plug slot contact structure for transistor performance enhancement

ABSTRACT

A method for forming a slot contact structure for transistor performance enhancement. A contact opening is formed to expose a contact region, and a slot contact is disposed within the contact opening in order to induce a stress on an adjacent channel region. In an embodiment, a stress inducing barrier plug is disposed within a portion of the contact opening and the remainder of the contact opening is filled with a lower resistivity contact metal. By selecting the proper materials and deposition parameters, the slot contact can be tuned to induce a tensile or compressive stress on the adjacent channel region, thus being applicable for both p-type and n-type devices.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/648,098, filed on Dec. 29, 2006, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor processing,and more specifically to novel contact structures and their method offabrication.

2. Discussion of Related Art

Well-recognized improvements in performance, functionality and economyof manufacture have led to integrated circuit designs at extreme levelsof device density and reduced size of electronic structures andconductive interconnections between them. As integrated circuits becomesmaller, the integrated circuit speed becomes dependent not only on thetransistor but also on the interconnecting pattern.

Historically, continuous performance enhancement of integrated circuitdesign has been dictated by the advancement of optical photolithographytools and photoresist materials. However, as CMOS device size progressesfurther into the nano-sized regime, the associated cost of these newtools and materials can be prohibitive. And in addition to economicconstraints, scaling is also quickly approaching constraints of devicematerials and design. Fundamental physical limits such as gate oxideleakage and source/drain extension resistance make continuedminimization difficult to maintain.

Accordingly, researchers have actively sought out methods other thanscaling to increase device performance. For example, researchers haveincreased device performance with implementation of silicon-on-insulatorsubstrates, high-k gate dielectrics, and metal gates. Researchers havealso investigated mobility enhancement in strained silicon as a methodto improve CMOS performance. One proposed method has been to globallystrain the silicon channel with a silicon-germanium virtual substrate.However, silicon-germanium virtual substrates are costly to manufacture.Another proposed method has been to locally strain the silicon channelwith selectively deposited lattice-mismatched source and drain regions.

At present, most CMOS circuit manufacturers employ a contact via holeplug for connecting one terminal of a CMOS component to a metallicinterconnect layer. Two advantages of the tungsten via hole plug overother materials are that tungsten may be deposited by CVD and alsotungsten has relatively low electromigration into the surroundingsilicon. However, tungsten also has a relatively high resistivitycompared to metals typically employed in interconnect layers, such ascopper. Accordingly, while tungsten is a favorable material for via holeplugs, its lateral resistance makes tungsten unfavorable as aninterconnect metal. Thus, there remains a need for an integrated contactstructure that both can increase device speed without adding additionalsteps and/or cost to manufacture, and also function as an interconnectlayer without unfavorable lateral resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional front view of an exemplary slotcontact structure implemented with a surface channel MOSFET.

FIG. 2 illustrates a top view of the exemplary slot contact structure ofFIG. 1.

FIG. 3 illustrates a top view of an exemplary slot contact structureconnecting at least two transistors.

FIG. 4 is a table providing experimental data of contact lineresistivity for slot contact lines of varying width.

FIG. 5A illustrates a cross-sectional front view of an exemplarysubstrate, gate stack structure, and channel region in accordance withthe present invention.

FIG. 5B illustrates a cross-sectional front view of formation of tipregions in accordance with the present invention.

FIG. 5C illustrates a cross-sectional front view of formation ofdielectric spacers and source and drain regions in accordance with thepresent invention.

FIG. 5D illustrates a cross-sectional front view of diffused tip andsource and drain regions in accordance with the present invention.

FIG. 5E illustrates a cross-sectional front view of the formation ofrecessed contact regions in accordance with the present invention.

FIG. 5F illustrates a cross-sectional front view of dielectric layersdisposed over the device of FIG. 5E.

FIG. 5G illustrates a cross-sectional front view the formation of acontact opening in the dielectric layers of FIG. 5F.

FIG. 5H illustrates a cross-sectional front view the formation of anadhesion layer and barrier plug disposed in the opening of FIG. 5G.

FIG. 5I illustrates a cross-sectional front view of an exemplary slotcontact structure with the remaining portion of the opening of FIG. 5Hfilled with a contact metal.

FIG. 6 is a table providing experimental data for intrinsic stressmeasurements of RF sputtered layers deposited on a silicon wafer at roomtemperature.

FIG. 7A illustrates a cross-sectional front view of a partiallycompleted transistor with diffused tip and source and drain regions inaccordance with the present invention.

FIG. 7B illustrates a cross-sectional front view of recess etched sourceand drain regions in accordance with the present invention.

FIG. 7C illustrates a cross-sectional front view of source and drainfilms disposed within the recess etched source and drain regions of FIG.7B.

FIG. 7D illustrates a cross-sectional front view of recess etched sourceand drain films in accordance with the present invention.

FIG. 7E illustrates a cross-sectional front view of an exemplary slotcontact structure in accordance with the present invention.

FIG. 8 illustrates a cross-sectional front view of an exemplary contactstructure embodied in a CMOS architecture.

DETAILED DESCRIPTION

In various embodiments, a novel slot contract structure and method offabrication is described with reference to figures. However, certainembodiments may be practiced without one or more of these specificdetails, or in combination with other known methods and materials. Inthe following description, numerous specific details are set forth, suchas specific materials, dimensions and processes, etc., in order toprovide a thorough understanding of the present invention. In otherinstances, well-known semiconductor processes and manufacturingtechniques have not been described in particular detail in order to notunnecessarily obscure the present invention. Reference throughout thisspecification to “an embodiment” means that a particular feature,structure, material, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention.Thus, the appearances of the phrase “in an embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, materials, or characteristics may be combined in anysuitable manner in one or more embodiments.

Embodiments of the present invention are directed towards a slot contactstructure and method of fabrication in which the slot contact induces astress on a device active region. Unlike the commonly employed via holecontact plug, in which the dimensions are determined by resolutionlimits of the lithographic wavelength employed, the slot contactembodiments of the present invention are described by a length and widthtailored to be relative to device dimensions.

In one aspect, embodiments of the invention provide a slot contact thathas a sufficient length and width to effectively induce a stress on anactive device region, thereby increasing device performance. Forexample, when the device is a surface channel MOSFET, embodiments of thepresent invention provide slot contacts to the source and drain regions,the contacts being described by a length that runs along the width ofthe MOSFET. Where the width of the MOSFET is large, likewise the lengthof the slot contact is large so that the slot contact may effectivelyinduce a stress across approximately the entire width of the MOSFET. Inan embodiment, the slot contact is approximately as long as a singleMOSFET width. The slot contact may also spread across multiple MOSFETdevices. For example, in other embodiments, the slot contact is two,three, or four times longer than a single MOSFET width.

The slot contacts may be disposed in recessed source and drain regions.Alternatively, the slot contacts may be disposed on raised source anddrain regions. Recessed source and drain regions allow for the lowerportion of the slot contact to be adjacent to the device channel regionso that the slot contact may more effectively induce a stress on thechannel region. For example, where the device is a surface channelMOSFET, the active channel region of the device is directly below thegate oxide. Therefore, some embodiments described herein provide astress inducing slot contact that extends below the gate dielectriclayer such that a portion of the slot contact is adjacent to the devicechannel region and the slot contact may effectively induces a stress onthe channel region. Accordingly, in certain embodiments, the MOSFETsource and drain regions are recessed prior to formation of the stressedslot contacts.

The slot contacts may also be disposed on raised source and drainregions. When the source and drain regions are raised, the lower portionof the slot contact is above rather than adjacent to the device channelregion and the slot contact may not effectively induce a stress on thechannel region. Since NMOS and PMOS devices behave with opposite signunder applied transverse stress, a designer may want to increase thestress on one type of device (for example NMOS) and reduce the stress onthe other type of device (for example PMOS). In an embodiment, this isaccomplished by forming a slot contact in recessed source and drainregions for one device (for example NMOS) and forming a slot contact onraised source and drain regions for another device (for example PMOS).

In another aspect, embodiments of the invention provide a slot contactthat may also function as an interconnect. The slot contact may becomprised of multiple materials. For example, the slot contact structuremay comprise a stress inducing barrier plug in the lower portion, withthe remainder of the slot contact structure being comprised of a lowresistance contact metal. In some embodiments, the barrier plug isprimarily responsible for inducing a stress on the device active region.However, the barrier plug may also possesses too high a resistivity tofunction as an interconnect metal. Thus, in a preferred embodiment, theslot contact is comprised of a minimum amount of higher resistancestress inducing barrier plug in the lower portion adjacent to the deviceactive region, and the remainder of the slot contact is comprised of amaximum amount of low resistance contact metal.

Long channel drive gains of approximately 8% have been realized for bothNMOS and PMOS devices employing embodiments of the present invention.While many embodiments herein are described in reference to a surfacechannel MOSFET device, this invention is also applicable to additionalsemiconductor devices such as, but not limited to, buried channeldevices, MISFET, and non-planar devices such as FinFET and Tri-Gate. Inaddition, embodiments of the stress inducing slot contact structureprovided herein are compatible with other stress inducing mechanismssuch as, but not limited to, a stress inducing etch stop layer,selectively deposited lattice-mismatched source and drain regions, andstress inducing isolation regions. It will become apparent that bycontrolling slot contact location, size, and shape, that a slot contactcan be created with the necessary dimensions and location relative tothe device to stress the device active region.

FIG. 1 illustrates an exemplary slot contact structure implemented witha surface channel MOSFET. Surface channel transistor 120 is formed on asubstrate 100. Any well-known substrate, such as but not limited to, amonocrystalline silicon or silicon on insulator can be used. In anembodiment substrate 100 comprises an epitaxial monocrystalline siliconlayer formed on a monocrystalline wafer. The monocrystalline layer mayalso be doped. For example, where transistor 120 is a p-type device, themonocrystalline layer may include an n-type dopant. Where transistor 120is an n-type device, the monocrystalline layer may include a p-typedopant. Isolation regions 104 are also formed in substrate 100.Isolation regions 104 may, for example, be shallow trench isolationregions. Isolation regions 104 may also be stressed and may be stressedin a way to optimally interact with the stress of the contact slotstructure.

Gate dielectric 112 and gate electrode 114 comprise the gate stack 110of transistor 120. Gate stack 110 defines channel region 116 thereunder.Dielectric spacers 118 are disposed along the sidewalls of the gatestack 110 and the upper surface of substrate 100. For example,dielectric spacers 118 may be single or multiple layer L-shapeddielectric spacers, the formation of which is known in the art. The gatestack and/or the dielectric spacers may also be stressed and may bestressed in a way to optimally interact with the stress of the contactslot structure.

Transistor 120 may include tip regions 132 in addition to source anddrain regions 130. As shown in FIG. 1, tip regions 132 may extend belowgate stack 110. Contact regions 140 may be a conductive material suchas, but not limited to, nickel-silicide, cobalt-silicide,titanium-silicide, or any refractory metal silicide.

Dielectric layer 154 is disposed over transistor 120. Dielectric layer154 may be silicon dioxide, possibly doped with phosphorus,boron/phosphorus, or arsenic, or alternatively low-k materials such as,but not limited to, carbon doped silicon dioxide or fluorinated oxide.Dielectric layer 154 is typically planarized. Additional dielectriclayers may also be disposed over transistor 120. For example etch stoplayer 152 may optionally be disposed over transistor 120 prior todisposing dielectric layer 154. Slot contacts 168 are formed indielectric layer 154 and optional etch stop layer 152 so that slotcontacts 168 make contact with contact regions 140. The dielectriclayers may also be stressed and may be stressed in a way to optimallyinteract with the stress of the contact slot structure.

As shown in FIG. 1, slot contact 168 has a top surface approximatelylevel with the top planarized surface of dielectric layer 154, a bottomsurface in contact with a portion of contact region 140, and sidewalls.In a specific embodiment, slot contact 168 has a width (C_(W)) that isapproximately 0.5 to 2 times as wide as the transistor 120 gate length(G_(L)), and slot contact 168 has a height approximately 3 to 4 timesthe transistor 120 gate length (G_(L)). For example, where transistor120 has a 45 nm gate length, slot contact 168 may have an 80 nm width(C_(W)) at the top of dielectric layer 154 and a 160 nm height. In anembodiment, slot contact 168 sidewalls are tapered. It is not uncommonfor a slight taper to be present even when dielectric layer 154 andoptional layer 152 are isotropically etched. As a result, slot contact168 may have a width (C_(W)) at the top of dielectric layer 154 that isdifferent from where slot contact 168 contacts contact region 140. Inone embodiment, slot contact 168 has a width (C_(W)) at the top ofdielectric layer 154 that is approximately twice as wide as where slotcontact 168 contacts contact region 140. In a specific embodiment, whentransistor 120 has a 45 nm gate length, and slot contact 168 has an 80nm width (C_(W)) at the top of dielectric layer 154 and a 160 nm height,slot contact 168 may have a 35 nm width (C_(W)) where slot contact 168contacts contact region 140.

In one embodiment, source and drain regions 130 are recess etched. Forexample, source and drain regions 130 may be etched in a source drainwet clean process where the wet clean facets the source and drainregions 130 and recesses them. Contact regions 140, such as, but notlimited to, nickel-silicide, cobalt-silicide, titanium-silicide, or anyrefractory metal-silicide, are then formed within the recessed sourceand drain regions 130. In an embodiment, slot contact 168 contacts thecontact region 140 at a location below the gate dielectric layer 112 ofgate stack 110. The depth of the location below the gate dielectriclayer may depend on a variety of factors such as device dimensions,depth of channel region 116, and amount of stress to be induced onchannel region 116. For a surface channel transistor, in order to mosteffectively induce a stress on channel region 116, slot contact 168 mustbe adjacent to the channel region 116, which means slot contact 168 mustcontact the contact region 140 at a sufficient depth below gatedielectric 112.

In an embodiment, when device 120 is a surface channel transistor, thelocation where slot contact 168 contacts the contact region 140 is adistance approximately 1% to 100% of the gate length (G_(L)) below gatedielectric layer 112. For example, in a specific embodiment when surfacechannel transistor 120 gate length is 45 nm, slot contact 168 contactscontact region 140 approximately 300 angstroms below gate dielectriclayer 112, which is approximately 67% of the gate length. In anotherembodiment, between approximately 10% and 25% of the total height forslot contact 168 is located below gate dielectric layer 112. In aspecific embodiment, 300 angstroms of a slot contact 168 with 160 nmheight is located below gate dielectric layer 112, which isapproximately 19% of the slot contact 168 height.

In some embodiments, slot contact 168 is comprised of barrier plug 164and contact metal 166. Slot contact 168 may further comprise adhesionlayer 162. In some embodiments, barrier plug 164 is largely concentratedin the bottom portion of slot contact 168. The amount of barrier plug164 present is dependent on device dimensions, contact architecture,amount of stress to be induced on channel region 116, and allowablelateral resistance. In one embodiment, barrier plug 164 comprises lessthan 50% of the total volume of slot contact 168. In another embodiment,barrier plug 164 comprises less than approximately 25% of the totalvolume of slot contact 168.

In a specific embodiment, when transistor 120 has a 45 nm gate lengthand slot contact 168 has an 80 nm width at the top of dielectric layer154 and a 160 nm height, barrier plug 164 may comprise approximately 300angstroms of the bottom portion of slot contact 168 and approximately 70angstroms of each sidewall. When an adhesion layer 162 is present,however, adhesion layer 162 may comprise a uniform 25 to 150 angstromsof the outermost bottom and sidewalls of slot contact 168. In anotherembodiment, adhesion layer may comprise a uniform 100 to 150 angstromsof the outermost bottom and sidewalls of slot contact 168. In a specificembodiment, barrier plug 164 and adhesion layer 162 together maycomprise approximately 300 angstroms of the bottom portion of slotcontact 168. The amount of each material will vary based on a variety offactors, such as, but not limited to, slot contact geometry and amountof stress to be induced.

In an embodiment, barrier plug 164 induces a stress on channel region116. In another embodiment, barrier plug 164 is intrinsically stressedand induces a stress on channel region 116. For example, where barrierplug 164 is intrinsically tensile, barrier plug 164 induces a tensilestress on channel region 116. When barrier plug 164 is intrinsicallycompressive, barrier plug 164 induces a compressive stress on channelregion 116. It is to be appreciated that barrier plug 164 mosteffectively induces a stress on channel region 116 when barrier plug 164is adjacent to channel region 116. Thus, the further barrier plug 164 iseither above or below channel region 116, the less effectively barrierplug 164 will induce a stress on channel region 116.

In one embodiment, barrier plug 164 and optional adhesion layer 162 fillthe portion of slot contact 168 below the dielectric layer 112 fortransistor 120 and are adjacent to channel region 116. In anotherembodiment, as shown by the dashed lines in FIG. 1, barrier plug 164fills a portion of slot contact 168 both above and below the dielectriclayer 112. In a specific embodiment where transistor 120 has a 45 nmgate length and slot contact 168 has an 80 nm width at the top ofdielectric layer 154 and a 160 nm height, barrier plug 164 comprisesapproximately 300 angstroms of the bottom portion of slot contact 168and barrier plug 164 is adjacent to channel region 116.

Stress inducing contact structure embodiments of the present inventionare compatible with CMOS architecture. For example, as shown in FIG. 8,the source and drain regions of one device (for example PMOS) may beraised to minimize the slot contract stress on the device while thesource and drain of the other device (for example NMOS) may be recessedto maximize the contact stress on the device.

In one embodiment, as shown in FIG. 8, a slot contact 868 is formedwithin recessed source and drain region 830 of transistor 820. Slotcontact 868 contacts the contact region 840 at a location below the gatedielectric layer 812 for transistor 820. As shown in FIG. 8, barrierplug 864 (and optional adhesion layer) fills the portion of slot contact868 below the gate dielectric layer 812 for transistor 820 and isadjacent to channel region 816. In another embodiment, barrier plug 864fills a portion of slot contact 868 both above and below the gatedielectric layer 812 for transistor 820.

In one embodiment, also shown in FIG. 8, slot contact 868 is formed onraised source and drain film 834 of transistor 821. Slot contact 868contacts the contact region 841 at a location above the gate dielectriclayer 813 for transistor 821, and therefore barrier plug 865 (andoptional adhesion layer) is above channel region 817 rather thanadjacent to channel region 817. Accordingly, barrier plug 865 may noteffectively induce a stress on channel region 817.

FIG. 2 illustrates a top view of the exemplary slot contact structure ofFIG. 1, wherein the length and width nomenclature for the exemplary slotcontact structure and transistor are described. FIG. 2 shows transistor220 (which is comprised of gate stack 210, dielectric spacers 214, andcontact regions 240) slot contact 268 (which is comprised of barrierplug 264, optional adhesion layer (not shown) and contact metal 266) andisolation regions 204.

As shown in FIG. 2, the gate length (G_(L)) is defined by the length ofgate stack 210 in the dimension between transistor 220 source and drainregions. The gate width (G_(W)) is defined by the width of gate stack210. This is typically in the dimension that determines the total poweror total current flow between the source and drain regions of transistor220. Slot contact 268 has a length and width nomenclature reversed fromthat of transistor 220. As shown in FIG. 2, the slot contact length(C_(L)) is defined by the length of slot contact 268 in the direction ofgate width. The slot contact width (C_(W)) is defined by the width ofslot contact 268 in the direction of gate length.

As shown in FIG. 2, slot contact 268 may be approximately as long as thewidth of transistor 220 so that slot contact 268 is able to induce astress across the entire width of transistor 220. Additionally, slotcontact 268 may be longer that the width of transistor 220. In anotherembodiment, slot contact 268 is two, three, or four times longer than asingle transistor 220 width. In other embodiments, slot contact 268 maybe considerably longer depending on device layout.

Slot contact 268 width (C_(W)) may also be tailored to the dimensions oftransistor 220. In one embodiment, slot contact 268 width (C_(W)) isapproximately two times the transistor 220 gate length (G_(L)). In aspecific embodiment where transistor 120 has a 45 nm gate length, slotcontact 168 has an 80 nm width. In another embodiment, slot contact 268is has a contact width (C_(W)) more than two times the transistor 220gate length (G_(L)). The wider slot contact 268 is, the more stress slotcontact 268 may induce on an adjacent channel region 116. In oneembodiment, where slot contact 268 includes a stress inducing barrierplug 164, the wider slot contact 268 is the more stress inducing barrierplug 164 is present to induce a stress on adjacent channel region 116.

FIG. 3 illustrates another embodiment of this invention where slotcontact 368 also function as an interconnect between at least twotransistors 320. As shown in FIG. 3, slot contacts 368 may additionallyspan across and make contact with isolation region 304 located betweentransistors 320. For example, isolation region 304 may be a shallowtrench isolation or LOCOS. In one embodiment, as shown in FIG. 3, slotcontact 368 length (C_(L)) spans across at least two transistors 320.

The ratio of barrier plug 364 to contact metal 366 is an importantvariable for controlling the resistivity of slot contact structure 368.Slot contact width (C_(W)) is an important parameter for controllingthis ratio. In one embodiment slot contact width is greater than theminimum width determined by resolution limits of the lithographicwavelength employed. FIG. 4 provides resistivity measurements for slotcontact structures with different widths fabricated in accordance withembodiments of this invention. As shown, slot contact structures with 40nm, 60 nm, and 76 nm slot contact widths (C_(W)) were fabricated.Barrier plugs were comprised of a TaN and Ta bi-layer (TNT) whichcomprised approximately 300 angstroms (150 angstroms each) of the bottomportion of slot contact and approximately 70 angstroms of each sidewall(35 angstroms each). The remainder of the slot contacts were comprisedof Cu contact metal. In each case resistivity measurements were reducedby greater than 80% compared to a slot contact comprised of a Ti/TiNadhesion layer (100 angstroms) and tungsten fill. The greater than 80%reduction in resistivity is attributed to the substitution of copper fortungsten as the primary conductive material in the slot contact. Smallvariations in the % reduction is considered noise among the samples.

Resistivity measurements for slot contact structures also decreased withincreasing slot contact width (C_(W)). This correlation can be accordedto the slot contacts with a larger width containing a larger volumeratio of low resistivity contact metal to higher resistivity barrierplug. Thus, the greater the amount of low resistivity contact metal inthe slot contact structure, the lower the lateral resistance, and hencethe motivation to confine the barrier plug to the area where the barrierplug can induce a stress into the device active region. In someembodiments, the volume of contact metal 366 is greater than the volumeof barrier plug 364 in the slot contact structure. In specificembodiments, the volume of contact metal 366 is greater than 75% of theoverall volume of slot contact 368. For example, where the contact metal366 is copper, slot contact 368 has an acceptable lateral resistance tofunction as an interconnect.

FIG. 5A illustrates a partially completed surface channel transistor.The process begins with a semiconductor substrate 500 having a topsurface 502. In one embodiment, semiconductor substrate is comprised ofa monocrystalline semiconductor layer having a top surface 502 formed ona monocrystalline wafer. The monocrystalline layer may, for example, bean epitaxial silicon layer formed on a monocrystalline silicon wafer,insulated substrate, or graded silicon-germanium virtual substrate.Substrate 500 may also be comprised of other well-known semiconductormaterials such as germanium and III-V materials such as, but not limitedto, InAs and GaAs. Substrate 500 may also be doped. For example,substrate 500 may include a monocrystalline layer with n-type welldopant where a p-type device is to be formed. Alternatively, substrate500 may include a a monocrystalline layer with p-type well dopant wherean n-type device is to be formed.

A plurality of isolation regions 504 are then formed in substrate 500.Isolation regions 504 isolate wells of different conductivity types, andisolate adjacent transistors. The isolation regions 504 may, forexample, be shallow trench isolation (STI) regions formed by etching atrench into substrate 500, and then filling the trench with depositedoxide.

A gate dielectric layer 512 is then formed on a top surface 502 ofsubstrate 500. The gate dielectric layer 512 may be a nitrided oxidelayer formed to a thickness of between 1 and 30 angstroms or may becomprised of a high-k dielectric material such as HfO₂ or anycombination of an oxide, nitrided oxide, or high-k dielectric material.A gate electrode 514 is then formed on the gate dielectric layer 512.Gate electrode 514 is preferable between 200 and 2,000 angstroms thick.In one embodiment, gate electrode may be formed by blanket deposition ofpolysilicon. The gate dielectric layer 512 and gate electrode 514 arethen patterned using known photolithographic techniques and etched toform gate stack 510, defining the channel region 516 thereunder. In anexemplary embodiment, the gate stack 510 has a gate length ofapproximately 45 nm.

FIG. 5B illustrates that dopant ions are then subsequently implantedinto an exposed upper surface of substrate 500 and into an exposed uppersurface of gate electrode 514. Tip regions 532 are formed in theimplanted region of substrate 500 on opposed sides of the gate stack510. Where the transistor is p-type, the dopant ions may, for example,be boron ions. Where the transistor is n-type, the dopant ions may, forexample, be phosphorus or arsenic.

FIG. 5C illustrates the formation of dielectric spacers 518 on opposingsides of the gate stack 510. Dielectric spacers 518 also cover portionsof the surface 502 adjacent and on opposing sides of the gate stack 510.In one embodiment, dielectric spacers 518 are formed by disposing aconformal insulating layer and anisotropically plasma etching it.Alternatively, dielectric spacers 518 may be multiple-layer L-shapedspacers, the formation of which is known in the art. Upper surfaces ofthe gate electrode 514 and the surface 502 are then again implanted withions, with the implantation energy increased over the step of FIG. 5B sothat the ions implant deeper into substrate 500 to form source and drainregions 530. The dielectric spacers 518 form a mask which preventsimplantation of the ions into tip regions 532 below the dielectricspacers 518.

A heat treatment or annealing step is subsequently carried out, whereinthe structure of FIG. 5C is heated. As shown in FIG. 5D, heating causesdiffusion of the tip regions 532 and source and drain regions 530 intolayer 500. Tip regions 532 diffuse slightly below the gate stack 510,and the lower edges of source and drain regions 530 move downward intosubstrate 500. Additionally, the doped region in gate electrode 514 alsodiffuses down to the gate dielectric layer 512.

FIG. 5E illustrates the formation of contact regions 540 on the sourceand drain regions 530. Contact regions 540 may be formed on the sourceand drain regions 530 using well-known processes. For example, suchprocesses may include blanket deposition of a metallic film such as, butnot limited to, Ni, Co, Ti, or any refractory metal. This is followed byan anneal step and selective removal of un-reacted metal (not shown),and possibly a second anneal. A hard mask (not shown), such as siliconnitride, may optionally be deposited on the gate stack 510 prior todeposition of the metallic film in order to shield the gate stack 510from contact formation. In some embodiments where substrate 500 includesa monocrystalline silicon layer, contact regions 540 may be, forexample, nickel-silicide, cobalt-silicide, titanium-silicide, or anyrefractory metal-silicide.

In another embodiment, the silicide process may be used to create ametal gate electrode architecture by fully siliciding the polysilicongate stack (commonly called FUSI). Silicide materials include, but arenot limited to nickel-silicide, cobalt-silicide, titanium-silicide, orany other refractory metal-silicide.

It is to be appreciated that embodiments of the present inventionprovide a slot contact that may induce a stress on an adjacent deviceactive region. Accordingly, in some embodiments, stress is mosteffectively transferred to the channel region 516 of transistor 520 whenthe lower portion of the slot contact is adjacent to channel region 116.Therefore, while forming completed transistor 520, it is to beappreciated that the location where the slot contact will connect tocontact region 540 is preferably adjacent to or below channel region516. Thus, for certain embodiments, as shown in FIG. 5E, a portion ofthe source and drain regions 530 are recessed below the originalsubstrate 500 surface 502, and are also recessed below the gate stack510.

In one embodiment, recessing the source and drain regions takesadvantage of the natural consumption of the monocrystalline substrate500 during silicidation of contact regions 540. Thus, in one embodiment,a portion of substrate 500 in the source and drain regions 530 isnaturally consumed. The natural consumption may result in the contactregions 530 being slightly recessed, with an upper surface of bothcontact regions 530 preferably below the gate stack 510.

In an alternative embodiment, source and drain regions 530 are recessetched prior to creation of contact regions 540. For example, source anddrain regions 530 may be selectively etched using an etchant whichselectively removes silicon over the other exposed materials of thestructure of FIG. 5E. Thus, recesses are thereby etched into regions530, and are aligned with the outer edges of dielectric spacers 518 andfield isolation regions 504. In many embodiments recesses are etchedisotropically. In one embodiment, a hydro-fluoride (HF) wet chemicaletch commonly employed in the pre-clean process to remove any residualnative oxide remaining on the source and drain contact areas can be usedto form faceted recesses in source and drain regions 530. In oneembodiment, source and drain regions 530 are recess etched, so thatafter formation of contact regions 540 a portion of the source and drain530 recessed surfaces are located approximately 1% to 100% of transistor520 gate length below the gate stack 510 and original surface 502. In aspecific embodiment, when transistor 520 has a 45 nm gate length, sourceand drain regions 530 are recess etched so that a portion of the sourceand drain 530 recessed surfaces are located approximately 350 to 400angstroms below the gate stack 510 and original surface 502. Afterformation of approximately 5 to 10 nm thick contact regions 540, aportion of contact regions 540 are then located approximately 300angstroms below the lower surface of gate stack 510 and original surface502.

FIG. 5F illustrates the formation of dielectric layers over transistor520. Firstly, a conformal dielectric layer 552 may optionally be formedover transistor 520 and substrate 500. For example, conformal dielectriclayer 552 may be a 10 to 200 nm thick Si₃N₄ or SiON etch stop/barrierlayer deposited by CVD. Additionally, layer 552 may induce a tensile orcompressive stress on transistor 520, the formation of which is known inthe art. In addition, a pad oxide (not shown) may be disposed prior tolayer 552 in order to alleviate stresses imparted to substrate 500 andtransistor 520.

Next, interlevel dielectric (ILD) layer 554 is disposed over transistor520 to provide insulation for the slot contacts and transistor 520. TheILD layer 554 is typically planarized using a chemical or mechanicalpolishing technique. Typically, for silicon-based semiconductor devices,dielectric materials for the ILD layer 554 are commonly silicon dioxide,possibly doped with phosphorus, boron/phosphorus, or arsenic, or low-kmaterials such as, but not limited to, carbon doped silicon dioxide orfluorinated oxide. All dielectric materials mentioned herein can bedisposed by well-known conventional processes to the typical thicknessemployed in this technology. ILD layer 554 is then planarized usingwell-known conventional processes such as chemical-mechanical-polishing.In a specific embodiment, when transistor 520 has a 45 nm gate length,ILD layer 554 is approximately 160 nm thick.

It is to be appreciated that embodiments of the invention are compatiblewith replacement gate electrode architecture, which is well-known in theart. While not described in detail, the structure of FIG. 5F can befollowed by a polish process which exposes the top surface of the gateelectrode. The gate is then removed, and an alternative gate material isadded. This gate material could be polysilicon, silicided polysilicon(include, but not limited to nickel-silicide, cobalt-silicide,titanium-silicide, or any other refractory metal-silicide), metal(including, but not limited to Ti, Al etc.) or a metal stack (including,but not limited to Ti, TiN, TiAl, and other metal alloys.)

FIG. 5G illustrates the formation of contact opening 556 in dielectriclayers 552 and 554 to expose contact region 540. In some embodiments,the exposed portion of contact region 540 is preferably adjacent to orbelow channel region 516. Thus, for certain embodiments, exposed portionof contact region 540 is below the gate stack 510. In one embodiment,the exposed portion of contact region 540 is located approximately 1% to100% of transistor 520 gate length below the gate stack 510. In aspecific embodiment, when transistor 520 has a 45 nm gate length, theexposed portion of contact region 540 is approximately 300 angstromsbelow gate stack 510.

Contact opening 556 is also defined by a length. In one embodiment, acontact opening is formed in dielectric layer 556, where the contactopening 556 has a length approximately as long as the width oftransistor 520. Additionally, contact opening 556 can be formed to belonger than the width of transistor 520. In another embodiment, contactopening 556 is two, three, or four times longer than a single transistor520 width. In other embodiments, contact opening 556 may be considerablylonger depending on device layout.

Conventional photolithographic techniques and anisotropic plasma etchingare used to form contact opening 556 in dielectric layer 554 and 552 toexpose contact region 540. It is to be appreciated that the slot contactto be formed in contact opening 556 is described by the same length andwidth as the contact opening 556. Notably, as shown in FIGS. 5G-5I,contact opening 556 may have a different width at the top planarizedsurface of dielectric layer 554 than where contact opening 556 exposescontact region 540. Thus, the contact opening 556 width andcorrespondingly the contact opening 556 length, may change from the topto the bottom. Accordingly, unless specifically referred to otherwise,the width of contact opening 556 and corresponding slot contact width(C_(W)), and length of contact opening 556 and corresponding slotcontact length (C_(L)), are in reference to the dimensions near the topplanarized surface of dielectric layer 554.

FIG. 5H illustrates the formation of an optional adhesion layer 562 andbarrier plug 564 within a portion of contact opening 556. In specificembodiments, adhesion layer 562 is disposed prior to disposing barrierplug 564 in order to provide a better surface for bonding and growth ofbarrier plug 564. As used herein, the terms barrier plug and adhesionlayer are not meant to be limited to single materials or single layers.In some embodiments, adhesion layer 562 and/or barrier plug 564 mayinclude multiple layers of different materials.

In some embodiments the barrier plug 564 fill process is such that it isa bottom-up fill process. The term bottom-up fill process as used hereinmeans that the deposition process is anisotropic, where more material isdeposited on the bottom of contact opening 564 than is deposited on asidewall of contact opening 556. In some embodiments, barrier plug 564is deposited using CVD techniques. In such embodiments the bottom-upfill process can be accomplished by controlling deposition temperature,pressure, and time. In other embodiments, barrier plug 564 is depositedusing PVD techniques, such as but not limited to, RF sputtering. In suchembodiments the bottom-up fill process can be accomplished bycontrolling deposition temperature, pressure, power, time, andre-sputter ratio.

The term re-sputter ratio as used herein, is defined as the ratio of thethickness of a film deposited on an unbiased substrate compared to thethickness of the film when deposited on a biased substrate. For example,applying a negative voltage to the substrate results in the depositingions knocking off already deposited ions, and hence a thinner film perunit time of deposition occurs than for a film deposited without thenegative voltage. Thus, when a sufficient negative voltage is applied tothe substrate during sputtering, the kinetic energy of the depositingions is also sufficient to sputter the film and redistribute it withinfeatures on the substrate. This leads to a thickening of the film in thebottom of contact opening 556. Accordingly, the re-sputter ratio is auseful variable for tuning a bottom-up fill process into features withdiffering geometries and aspect ratios.

Additionally, the bottom-up fill approach can be assisted by controllingthe dimensions of contact opening 556. In particular, and as shown inFIG. 5G, contact opening 556 may have tapered sidewalls, where the widthof contact opening 556 is greater at the top planarized surface ofdielectric layer 554 than where contact opening 556 exposes contactregion 540. In such a case, the narrower width at the bottom of contactopening 556 assists the bottom-up fill process where more material isdeposited on the bottom than on the sidewalls contact opening 556.

In an embodiment, slot contact 568 induces a stress on channel region516. In another embodiment, barrier plug 564 of slot contact 568 inducesa stress on channel region 516. In a specific embodiment, barrier plug564 possesses an intrinsic tensile or compressive stress. Where barrierplug 564 is intrinsically tensile, barrier plug 564 will induce atensile stress on the channel region 516. A film deposited to possess anintrinsic tensile stress may relax by contracting, and by contractingthe film induces a tensile stress on the surroundings. Conversely, afilm deposited to possess an intrinsic compressive stress may relax byexpanding, and by expanding the film induces a compressive stress on thesurroundings. Thus, where barrier plug 564 is intrinsically compressive,barrier plug 564 induces a compressive stress on the channel region 516.

In one embodiment, barrier plug 564 is disposed within less than 50% ofthe total volume of contact opening 556. In another embodiment, barrierplug 564 is disposed within less than 25% of the total volume of contactopening 556. In one embodiment, barrier plug 564 is disposed withincontact opening 556 such that a portion of barrier plug 564 is belowgate dielectric layer 512. In yet another embodiment, barrier plug 564is disposed within contact opening 556 such that a first portion ofbarrier plug 564 is below gate dielectric layer 512 and a second portionof barrier plug 564 is above gate dielectric layer 512.

In one embodiment, barrier plug 564 is intrinsically compressive andinduces a compressive stress on channel region 516. Such intrinsicallycompressive plugs can serve to provide p-type transistor enhancement. Inone embodiment the intrinsically compressive barrier plug 564 iscomprised of a TaN and Ta (TNT) bi-layer. The TNT barrier plug 564induces a compressive stress on channel region 516, and also functionsto block migration of the subsequently deposited contact metal 566 (FIG.5I) into the surrounding dielectric layers.

In a specific embodiment, when transistor 520 has a 45 nm gate length, aTNT bi-layer barrier plug 564 is RF sputter deposited into a 160 nm highby 80 nm wide contact opening 556. In such an embodiment, a firstintrinsically compressive TaN film is RF sputter deposited into opening556. Deposition parameters are approximately room temperature 25 C,pressure of 1.6-1.8 mTorr, DC power at 10-20 kW, RF power at 300-700 W,and resputter ratio at 1.0-1.2. In one embodiment, an exemplary TaN filmfills approximately the bottom 10% of the total contact opening 556height. In such an embodiment, the TaN film may fill the bottom 150angstroms of contact opening 556 and be approximately 35 angstroms thickon the sidewalls of contact opening 556. The TaN film may have anintrinsic compressive stress of 1-4 E+10 dyne/cm2.

Following the TaN film, an intrinsically compressive Ta film is RFsputter deposited over the TaN film. Deposition parameters areapproximately room temperature 25 C, pressure of 0.3-0.8 mTorr, DC powerat 10-20 kW, RF power at 100-300 W, and resputter ratio at 1.0-1.2. Inone embodiment, an exemplary Ta film fills approximately the next 10% ofthe total contact opening 556 height, which is above the TaN film. Insuch an embodiment, an exemplary Ta film may fill the bottom 150angstroms of contact opening 556 remaining after deposition of the TaNfilm, and be approximately 35 angstroms thick on the new sidewalls ofcontact opening 556 after deposition of the TaN film. The Ta film mayhave an intrinsic compressive stress of 1-4 E+10 dyne/cm2. In such anembodiment, the composite TNT bi-layer barrier plug 564 is disposedwithin 10-25% of total height for contact opening 556. Thus, whencontact opening 556 is 160 nm high and 80 nm wide, the composite TNTbi-layer barrier plug 564 is, for example, approximately 300 angstromsthick at the bottom of contact opening 556 (˜19%) and approximately 70angstroms wide on the sidewalls of contact opening 556.

In one embodiment, a TNT bi-layer barrier plug 564 is disposed withincontact opening 556 such that a portion of TNT bi-layer barrier plug 564is below gate dielectric layer 512 and adjacent to channel region 516.In yet another embodiment, additional TNT bi-layer barrier plug 564 isdisposed within contact opening 556 such that a first portion of TNTbi-layer barrier plug 564 is below gate dielectric layer 512 and asecond portion of TNT bi-layer barrier plug 564 is above gate dielectriclayer 512.

FIG. 6 provides experimental data for intrinsic stress measurements ofRF sputtered layers deposited at room temperature on a silicon wafer.Stress measurements were obtained using the change in bow of the waferbefore and after film deposition according to Stoney's Equation. Asshown in FIG. 6, TaN, Ta, and TNT films RF sputter deposited at roomtemperature have an intrinsic compressive stress on the order of E+10dyne/cm2. In addition, FIG. 6 indicates that re-sputtering does notsignificantly affect resulting intrinsic stress. Measurements did notvary significantly from low bias deposition (low re-sputter ratio) andhigh bias deposition (high re-sputter ratio).

It is to be appreciated that sputter deposition temperature is acritical factor in controlling the intrinsic stress levels for barrierplug 556. For example, increasing the deposition temperature for the TNTbarrier plug 564 to about 400 C results in a reduction of the intrinsiccompressive stress to about 1-5 E+9 dyne/cm2.

FIG. 6 additionally provides measurements of the intrinsic stress for a500 angstrom thick electrolessly deposited Cu layer as being 6.19E+8dyne/cm2, which is slightly intrinsically tensile. This is two orders ofmagnitude less than the measured values on the order of E+10 dyne/cm2for the barrier plug materials. Accordingly, it is to be appreciatedthat that the intrinsic stress of barrier plug 564 should be greaterthan that of the contact metal 566. Where Cu is employed as contactmetal 566 (FIG. 1F), barrier plug 564, particularly when intrinsicallycompressive, preferably has an intrinsic stress of at least E+9 dyne/cmin order to drown out the effect of the intrinsic tensile Cu contactmetal 566 stresses.

In one embodiment, barrier plug 564 is intrinsically tensile and inducesa tensile stress on channel region 516. Such intrinsically tensilebarrier plugs could serve to provide n-type transistor enhancement. Inone embodiment, barrier plug 564 is CVD deposited tungsten (W) ortungsten nitride (WN), though other materials and methods can be used,such as but not limited to Mo and Cr. CVD tungsten is naturallyintrinsically tensile, typically on the order to E+10 dyne/cm2, thoughit can be made higher or lower. Generally, the lower the depositiontemperature, the more tensile tungsten will be, and the higher thedeposition temperature, the less tensile.

In some specific embodiments employing W or WN as barrier plug 564 itmay be necessary to deposit an adhesion layer first. In a specificembodiment, optional adhesion layer 562 is deposited prior to barrierplug 564, as shown in FIG. 5H. In a specific embodiment, adhesion layer562 is comprised of a Ti and TiN bi-layer. In one embodiment, adhesionlayer may have a thickness of approximately 5% to 10% of the contactopening 556 height, and 12% to 19% of contact opening 556 width. In aspecific embodiment where contact opening is 160 nm high and 80 nm wide,a first, 50-80 angstrom thick Ti layer is sputter deposited on thesurfaces of contact opening 556 at room temperature 25 C, 15-16 mTorr,and DC power of 1.8-2.0 kW. Although any available PVD technique issufficient. The Ti layer contacts the silicide contact region 540 at thebottom of contact opening 556. If a native oxide has formed on thesilicide, the Ti will reduce the oxide, and lower the contactresistance.

Next, a 50-70 angstrom thick TiN layer is deposited on the Ti layer withCVD at approximately 450 C and approximately 40 Torr using a tetradimethyl amino titanium (TDMAT) precursor. The TiN functions to cut offcontact off the Ti layer from the precursor used to deposit thesubsequent tungsten plug material 564. Together the Ti and TiN layerscomprise adhesion layer 562.

Then, a tungsten barrier plug 564 is deposited over adhesion layer 562using a bottom-up fill approach. In one embodiment, the tungsten barrierplug 564 is deposited using a WF₆H precursor in hydrogen ambient attemperature range of 325 C to 425 C and pressure of 30-50 mTorr. Thelower the deposition temperature, the more tensile the tungsten will be,and the higher the deposition temperature, the less tensile. In oneembodiment, an exemplary tungsten barrier plug 564 is disposed withinapproximately the next 9% to 13% of the total contact opening 556 heightlocated above the adhesion layer 562. In a specific embodiment, thetungsten barrier plug 564 is approximately 150 to 200 angstroms thick atthe bottom of opening 556 and approximately 70 angstroms wide near thesidewalls of opening 556. Depending on the desired structure, more orless tungsten barrier plug 564 may be deposited.

In one embodiment, a tungsten barrier plug 564 is disposed withincontact opening 556 such that a portion of the tungsten barrier plug 564is below gate dielectric layer 512 and adjacent to channel region 516.In yet another embodiment, additional tungsten barrier plug 564 isdisposed within contact opening 556 such that a first portion of thetungsten barrier plug 564 is below gate dielectric layer 512 and asecond portion of the tungsten barrier plug 564 is above gate dielectriclayer 512.

Finally, as shown in FIG. 5I, the remainder of opening 556 is filledwith a low resistance contact metal 566, such as, but not limited to,copper, in order to complete slot contact 568. In some embodimentscontact metal 566 is grown electrolytically or electrolessly. Wherecontact metal 566 is comprised of Cu, a low resistance material such asa Cu seed layer may first be sputtered onto barrier plug 564 in order toassist the plating process.

In some embodiments, the low resistance contact metal 566 will be theprincipal conductive material in the slot contact 568 providing a lowresistance contact to the source/drain contact region 540. In suchembodiments, the volume of contact metal 566 in slot contact 568 isgreater than the volume of barrier plug 564 in slot contact 568. Inspecific embodiments, the volume of contact metal 566 is greater than75% of the overall volume of slot contact 168. In another embodiment,contact metal 566 is disposed within the top 75% to 90% of the totalcontact opening 556 height.

FIGS. 7A-7E illustrate an alternative embodiment of the invention. FIG.7A illustrates a partially completed surface channel transistor 720.Similar to the structure described in FIG. 5D, transistor 720 includesdielectric spacers 718, and gate stack 710 defining channel region 716thereunder. Source and drain regions 730, tip regions 732, and isolationregions 704 may all be formed in substrate 700. In one embodiment,transistor 720 is a p-type transistor, substrate 700 is n-doped, andsource and drain regions 730 and tip regions 732 are p-doped.

FIG. 7B illustrates the formation of recesses in source and drainregions 730. For example, source and drain regions 730 may beselectively etched using an etchant which selectively removes siliconover the other exposed materials of the structure of FIG. 7B. Thus,recesses are thereby etched into regions 730, and are aligned with theouter edges of dielectric spacers 718 and field isolation regions 704.In many embodiments recesses are etched isotropically. In oneembodiment, a hydro-fluoride (HF) wet chemical etch can be used to formfaceted recesses in source and drain regions 730. In a specificembodiment, source and drain regions 730 may be recess etched so that aportion of the recessed surfaces are located approximately 1,000angstroms below the gate stack 710 and original surface 702.

FIG. 7C illustrates the formation of selectively deposited source anddrain films 734. Source and drain films 734 are expitaxially formed inthe recessed source and drain regions 730. In one embodiment, source anddrain films 734 are lattice mismatched with respect to substrate 100 inorder to transfer stress to channel region 716. For example, source anddrain films 734 include silicon, germanium, and are in situ doped withboron. Source and drain films 734 maybe epitaxially deposited using aCVD chamber with the following processing conditions: dicholorsiline of20 sccm, diborant of 70 sccm at 1% concentration, and germane of 50sccm, at a temperature of approximately 740 C. In one embodiment, thegermanium concentration in the source and drain films 734 isapproximately 15-20%. The larger lattice constant of the SiGe film mayinduce a compressive stress on channel region 716.

In one embodiment, it is preferred that source and drain films 734 areraised source and drain films, that the top surface is above the gateoxide in gate stack 710. In such an embodiment, the source and drainfilms 734 are raised to minimize the stress transfer from the slotcontact. In other embodiment, it is preferred to etch-back the sourceand drain films 734 so that a portion lies below the gate stack 710. Insuch an embodiment, the source and drain films 734 are recessed foroptimal stress transfer from the slot contact.

FIG. 7D illustrates source and drain films 734 recess etched below gatestack 710. In one embodiment, source and drain films 734 are recessetched, so that after formation of contact regions 740 a portion of thesource and drain films 734 recessed surfaces are located approximately1% to 100% of transistor 720 gate length below the gate stack 710 andoriginal surface 702. In a specific embodiment, when transistor 720 hasa 45 nm gate length, source and drain region films 734 are recess etchedso that a portion of the source and drain films 734 recessed surfacesare located approximately 350 to 400 angstroms below the gate stack 710and original surface 702. After formation of approximately 5 to 10 nmthick contact regions 740, a portion of contact regions 740 are thenlocated approximately 300 angstroms below the lower surface of gatestack 710 and original surface 702.

In an alternative embodiment, the structure in FIG. 7D can be obtainedby deposition of source and drain films 734 such that they onlypartially fill the recessed source and drain regions 730; as opposed todeposition of raised source and drain films (as in FIG. 7C) followed byrecess etch-back.

FIG. 7E illustrates completed transistor 720 and slot contacts 768,after formation of contact regions 740 and dielectric layers 752 and754. In one embodiment, slot contacts 768 make contact with contactregions 740 at approximately 1% to 100% of transistor 720 gate lengthbelow the gate stack 710 and original surface 702. In one embodiment,slot contacts 768 make contact with contact regions 740 at approximately300 angstroms below the lower surface of gate stack 710 and originalsurface 702. In an embodiment, source and drain films 734 are latticemismatched with respect to substrate 700. In one embodiment source anddrain films 734 induce a compressive stress on channel region 716, andslot contacts 768 also induces a compressive stress on channel region716. In an alternative embodiment, source and drain films 734 induce atensile stress on channel region 716, and slot contacts 768 also inducesa tensile stress on channel region 716.

Embodiments of the invention have been described herein where a contactstructure provides a stress in a device channel region therebyincreasing device performance. Specific embodiments have been measuredto increase long channel drive by approximately 8% in both NMOS (with aninduced tensile stress) and PMOS (with an induced compressive stress).Though when combined in CMOS architecture an intrinsically tensilestressed contact structure will provide an increase to the NMOS devicewhile degrading the PMOS device by the same amount. This degradation canbe prevented, however, by controlling the contact region location, size,shape, and by raising the source and drain regions of the PMOS device asshown in FIG. 8.

FIG. 8 illustrates an embodiment where both an NMOS and PMOS device areconnected in a CMOS architecture. Slot contacts 868 all comprise anintrinsically tensile barrier plug. The NMOS transistor 820 includessource and drain regions 830, and contract regions 840 that are slightlyrecessed into the source and drain regions 830. While it is not requiredthat the contact regions 840 are located below gate stack 810, it ispreferred that slot contact 868 touch the contact region 840 below thelevel of the gate stack 810 so that the contact structure 868 can mosteffectively induce a tensile stress on the active channel region 816.

The PMOS transistor 821 includes raised source and drain films 834. Forexample, source and drain films 834 can be fabricating by well-knownrecess etch and deposition methods of in situ doped silicon andgermanium. Contact regions 841 lie above gate stack 811 and activechannel region 817. Accordingly, contact structure 868, whileintrinsically tensile, does not induce a considerable tensile stress onthe active channel region 817 because of the location. Thus, thedegradation effect of the intrinsically tensile contact structure 868 isminimized in the PMOS device, and the same slot contact structure can beimplemented for integrated NMOS and PMOS devices.

Although the present invention has been described in language specificto structural features and/or methodological acts, it is to beunderstood that the invention defined in the appended claims is notnecessarily limited to the specific features or acts described. Thespecific features and acts disclosed are instead to be understood asparticularly graceful implementations of the claimed invention usefulfor illustrating the present invention.

1. A semiconductor structure comprising: a transistor including a gatestack and a silicided contact region, the gate stack defining a channelregion thereunder; and a slot contact in contact with a portion of thecontact region below the gate stack, the slot contact being at leasttwice as long as it is wide, the slot contact comprising anintrinsically stressed barrier plug and a contact metal disposed overthe intrinsically stressed barrier plug, the contact metal having alower resistivity than the intrinsically stressed barrier plug; whereina bottom thickness of the intrinsically stressed barrier plug comprisinga bottom portion of the slot contact is greater than a sidewallthickness of the intrinsically stressed barrier plug comprising asidewall portion of the slot contact, and the bottom thickness of theintrinsically stressed barrier plug is both above and below a gatedielectric layer of the gate stack such that the slot contact induces astress on the channel region.
 2. The structure of claim 1, wherein theslot contact is approximately as long as the transistor width.
 3. Thestructure of claim 1, wherein the slot contact is longer than thetransistor width.
 4. The structure of claim 1, wherein the volume of thecontact metal in the slot contact is greater than the volume of theintrinsically stressed barrier plug in the slot contact.
 5. Thestructure of claim 1, wherein at least 10% of the total slot contactheight is located below the gate stack.
 6. The structure of claim 1,wherein the intrinsically stressed barrier plug is intrinsicallytensilely stressed and induces a tensile stress on the channel region.7. The structure of claim 6, wherein the transistor is an NMOStransistor.
 8. The structure of claim 6, wherein the intrinsicallystressed barrier plug comprises tungsten.
 9. The structure of claim 1,wherein the intrinsically stressed barrier plug is intrinsicallycompressively stressed and induces a compressive stress on the channelregion.
 10. The structure of claim 9, wherein the transistor is a PMOStransistor.
 11. The structure of claim 9, wherein the intrinsicallystressed barrier plug comprises tantalum.
 12. The structure of claim 9,wherein the intrinsically stressed barrier plug comprises tantalumnitride.
 13. The structure of claim 9, wherein the intrinsicallystressed barrier plug comprises a tantalum nitride and tantalumbi-layer.
 14. The structure of claim 1, wherein the contact metalcomprises copper.
 15. The structure of claim 1, wherein the slot contactfurther comprises an adhesion layer below the intrinsically stressedbarrier plug.
 16. The structure of claim 15, wherein the adhesion layercomprises titanium.
 17. The structure of claim 15, wherein the adhesionlayer comprises titanium nitride.
 18. The structure of claim 15, whereinthe adhesion layer comprises a titanium and titanium nitride bi-layer.19. The structure of claim 1, wherein the silicided contact regioncomprises a refractory metal-silicide.
 20. The structure of claim 19,wherein the refractory metal-silicide is selected from the groupconsisting of nickel-silicide, cobalt-silicide and titanium-silicide.